1. Field of the Invention
The present invention relates to a positive or negative image-formation material which can be recorded image-wise by exposure to an infrared laser and in which solubility of a recording layer at exposed portions changes, and to an infrared absorber which can be suitably used in the image-formation material. More particularly, the present invention relates to an image-formation material with an infrared layer, which can be recorded by exposure to an infrared laser or the like in the near-infrared range, and particularly which is suitable for a planographic printing plate used for so-called direct plate formation which can provide plate formation directly from digital signals of computers and the like, and to an infrared absorber having a surface orientation group, which absorber is suitable for application in the image-formation material.
2. Description of the Related Art
Recently, with the development of solid lasers and semiconductor lasers having an emitting region in near-infrared to infrared ranges, systems using infrared lasers and providing direct plate formation from digital data of computers have drawn attention.
JP-A No. 7-285275 discloses a positive-type planographic printing material for infrared lasers used in direct plate formation. This invention is an image-recording material obtained by adding to an alkaline aqueous solution-soluble resin a substance which absorbs light and generates heat, and a positive photosensitive compound such as a quinonediazide compound or the like. The positive photosensitive compound acts in image portions as a solution inhibitor that substantially decreases solubility of the alkaline aqueous solution-soluble resin, and is decomposed in non-image portions by heat, leading to a loss of solution-inhibiting ability. Resultantly, the positive photosensitive compound can be removed by development, to form an image.
On the other hand, it is known that onium salts and alkali-insoluble compounds which can form hydrogen bonds act to suppress alkali-solubility of an alkali-soluble polymer. Regarding an image-formation material for infrared lasers, WO97/39894 describes that a composition using a cationic infrared absorber as an agent to suppress dissolution of an alkaline water-soluble polymer shows a positive action. This positive action is such that an infrared absorber absorbs laser light and an effect of suppressing dissolution of a polymer film at irradiated portions is reduced by generated heat, to form an image.
Further, as a method for forming negative images, there is a recording method in which a polymerization reaction is allowed to occur using, as an initiator, radicals generated by light or heat. The reaction cures a recording layer at exposed portions, forming image portions. Regarding such printing plates having a recording layer which is polymerized by light or heat, there are known technologies using, as a photosensitive layer, photopolymerizable or heat-polymerizable compositions as described in JP-A Nos. 8-108621 and 9-34110.
Regarding image-forming properties of the above-mentioned various recording materials, there is a problem in that, although energy sufficient for an image formation reaction is obtained at the surface of a sensitive material irradiated by a laser, thermal diffusion to a substrate is extensive, due to excellent thermal diffusion, and particularly due to excellent heat conductivity when a generally-used aluminum substrate is used as the substrate. Consequently, energy is not sufficiently utilized for forming images, leading to low sensitivity. With this problem, a sufficient effect of reducing suppression of dissolution or an effect of promoting a reaction by polymerization may not be obtained in deep portions of the sensitive material. Consequently, the occurrence of alkali development at exposed portions/non-exposed portions may not be fully realized, such that excellent images cannot be obtained, and furthermore, developing latitude, that is, tolerable range which can afford good image-formation when concentration of an alkaline developing solution is varied, is narrow.